This research asks three major questions about long term fertility decline. 1. Whether irreversible fertility decline can occur under extremely primitive economic and social conditions such as feudalism, whether that decline is occasioned by economic development or by immiseration, and whether the influences of a market economy accelerate such decline. 2. Whether fertility decline, either short or long term, is driven primarily by economic forces or constrained by cultural and linguistic ones. 3. Whether and how alternative mechanisms for achieving population:resource balance, e.g. nuptiality control, fertility control, and migration, are related. 4. The way in which household and kinship support structures affect survival and fertility behavior. The research will use one of the largest computer-readable family reconstitution data sets known -- about 220,000 births, marriages and deaths to c. 40,000 families in 7 contiguous parishes of southeastern Croatia c. 1700-1900. Preliminary work shows fertility responded positively to increased resources and declined under land shortage. Both fertility control and emigration occur as responses to shortage. Long term decline begins as early as 1780, under feudalism, concentrated among wealthier serfs and those most subject to market influences and competition for common land. This research will develop new techniques of missing data imputation. It will analyze genealogical linkages and treat joint and extended families as producer-consumer units. It will assess the relative importance of economic and cultural factors, using rich ethnographic and linguistic data at the village level and will compare data from this study to information from other populations in the same region and will incorporate macrolevel information into micro-regional household level analysis. Special attention will be given to the effects of household composition and kinship networks on fertility control, lactation and surrogate nursing, and maternal and child survival, primarily through hazard analysis in which such familial and kinship data are covariates. Maternal deaths will be imputed from peaks in the timing of postpartum deaths. This analysis will throw new light on the conditions under which fertility decline began to emerge even under feudal economic and political conditions. The comparison of the importance of cultural and linguistic determinants as against economic determinants will be relevant not only to current theoretical debate but also to understanding probable developments in LDCs.